Electronic device including sub-array based deblurring of a blurred finger image and related methods

ABSTRACT

An electronic device may include a finger biometric sensor that includes an array of electric field sensing pixels and image data output circuitry coupled thereto and capable of processing the image data from each of sub-arrays of the array of electric field sensing pixels. The electronic device may also include a dielectric layer over the array of electric field sensing pixels and causing electric field diffusion so that the image data output circuitry generates image data corresponding to a blurred finger image. The electronic device also includes deblurring circuitry coupled to the image data output circuitry and capable of processing the image data from each of the plurality of sub-arrays of the array of electric field sensing pixels to produce processed image data representative of a deblurred finger image.

FIELD OF THE INVENTION

The present invention relates to the field of electronics, and, moreparticularly, to electronic devices including finger biometric sensorsand related methods.

BACKGROUND OF THE INVENTION

Fingerprint sensors that measure the fingerprint pattern using electricfield sensing methods and capacitive sensing methods have become wellestablished. U.S. Pat. Nos. 5,940,526 and 5,963,679 are examples of thistype of fingerprint sensor, the entire contents of which areincorporated herein by reference. These systems measure the fingerprintpattern by generating an electric field between the finger and thesensor array, and measuring the spatial fluctuations in field strengthat the sensor array caused by the shape of the fingerprint ridge andvalley pattern.

In some recent applications, it may be desirable to capture images offingerprint patterns from fingers that are farther away from the sensorarray than is typical with today's technologies. Unfortunately, as thefinger gets farther away from the sensor array, for example when arelatively thick dielectric lies between the sensor array and thefinger, the relatively thick dielectric between the sensor array and thefinger may cause variations in the electric field between the finger andthe sensor array. These variations may cause image data generated by thefinger sensor to be representative of a blurred image.

SUMMARY

An electronic device may include a finger biometric sensor that includesan array of electric field sensing pixels and image data outputcircuitry coupled thereto and is capable of outputting image data from aplurality of sub-arrays of the array of electric field sensing pixels.The electronic device may also include a dielectric layer over the arrayof electric field sensing pixels and causing electric field diffusion sothat the image data output circuitry generates image data correspondingto a blurred finger image. The electronic device may further includedeblurring circuitry coupled to the image data output circuitry andcapable of processing the image data from each of the plurality ofsub-arrays of the array of electric field sensing pixels to produceprocessed image data representative of a deblurred finger image.Accordingly, the electronic device deblurs a blurred finger image causedby electric field diffusion from the dielectric layer.

The plurality of sub-arrays may include at least one sub-array adjacenta border of the array, for example. The plurality of sub-arrays may alsoinclude at least one internal sub-array spaced inwardly from a border ofthe array.

The electric field diffusion has a diffusion function associatedtherewith. The deblurring circuitry may be capable of processing theimage data in accordance with respective deblurring functions for eachof the plurality of sub-arrays based upon the diffusion function, forexample.

The diffusion function may include a Gaussian function, and therespective deblurring functions may each include an inverse Gaussianfunction. The deblurring circuitry may be capable of storing a pluralityof deblurring coefficients for each of the respective deblurringfunctions.

The dielectric layer may have a non-uniform thickness, for example. Thedeblurring circuitry may be capable of processing the image data toproduce image data representative of the deblurred finger image basedupon the non-uniform thickness. The deblurring circuitry may include adeblurring processor and memory coupled thereto and capable of storingthe image data.

The finger biometric sensor may further include drive circuitry coupledto the array of electric field sensing pixels. The finger biometricsensor may include a finger coupling electrode adjacent the array ofelectric field sensing pixels and coupled to the drive circuitry, forexample.

A method aspect is directed to a finger biometric method includingoperating a finger biometric sensor that may include an array ofelectric field sensing pixels and image data output circuitry coupledthereto and capable of outputting image data from a plurality ofsub-arrays of the array of electric field sensing pixels, and with adielectric layer over the array of electric field sensing pixels therebycausing electric field diffusion so that the image data output circuitrygenerates image data corresponding to a blurred finger image. The methodmay also include processing the image data using deblurring circuitrycoupled to the image data output circuitry to produce, from each of theplurality of sub-arrays of the array of electric field sensing pixels,processed image data representative of a deblurred finger image.

A non-transitory computer readable medium for finger biometricprocessing may include computer-executable instructions capable ofperforming operations. The operations may include operating a fingerbiometric sensor that includes an array of electric field sensing pixelsand image data output circuitry coupled thereto and capable ofoutputting image data from a plurality of sub-arrays of the array ofelectric field sensing pixels, and with a dielectric layer over thearray of electric field sensing pixels thereby causing electric fielddiffusion so that the image data output circuitry generates image datacorresponding to a blurred finger image. The operations may also includeprocessing the image data using deblurring circuitry coupled to theimage data output circuitry to produce, from each of the plurality ofsub-arrays of the array of electric field sensing pixels, processedimage data representative of a deblurred finger image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an electronic device according to the presentinvention.

FIG. 2 is a schematic block diagram of the electronic device of FIG. 1.

FIG. 3 is a more detailed schematic block diagram of a portion of theelectronic device of FIG. 1.

FIG. 4 is a schematic cross-section of a portion of a dielectric layercovering the array of electric field sensing pixels in accordance withthe present invention.

FIG. 5a is a blurred finger image caused by a dielectric layer, forexample, as illustrated in FIG. 4.

FIG. 5b is a deblurred finger image processed by the deblurringcircuitry of the electronic device of FIG. 3.

FIG. 6 is a schematic block diagram of an electronic device inaccordance with another embodiment.

FIG. 7 is a more detailed schematic block diagram of a portion of theelectronic device in of FIG. 6.

FIG. 8a illustrates a portion of a blurred finger image processedaccording to a deblurring function in accordance with an embodiment.

FIG. 8b illustrates a border portion of a blurred finger image processedaccording to a deblurring function in accordance with an embodiment.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

Referring initially to FIGS. 1-3, an electronic device 20 is nowdescribed. The electronic device 20 illustratively includes a portablehousing 21 and a processor 22, for example a host processor, carried bythe portable housing. The electronic device 20 is illustratively amobile wireless communications device, for example, a cellulartelephone. The electronic device 20 may be another type of electronicdevice, for example, a tablet computer, laptop computer, etc.

Wireless communications circuitry 25 (e.g. a wireless transceiver,cellular, WLAN Bluetooth, etc.) is also carried within the housing 21and coupled to the processor 22. The wireless transceiver 25 cooperateswith the processor 22 to perform at least one wireless communicationsfunction, for example, for voice and/or data. In some embodiments, theelectronic device 20 may not include a wireless transceiver 25.

A display 23 is also carried by the portable housing 21 and is coupledto the processor 22. The display 23 may be a liquid crystal display(LCD), for example, a touch screen display, or may be another type ofdisplay, as will be appreciated by those skilled in the art. A devicememory 26 is also coupled to the processor 22.

A finger-operated user input device, illustratively in the form of apushbutton switch 24, is also carried by the portable housing 21 and iscoupled to the processor 22. The pushbutton switch 24 cooperates withthe processor 22 to perform a device function in response to thepushbutton switch. For example, a device function may include a poweringon or off of the electronic device 20, initiating communication via thewireless communications circuitry 25, and/or performing a menu function.

More particularly, with respect to a menu function, the processor 22 maychange the display 23 to show a menu of available applications basedupon pressing of the pushbutton switch 24. In other words, thepushbutton switch 24 may be a home switch or button, or key. Of course,other device functions may be performed based upon the pushbutton switch24. In some embodiments, the finger-operated user input device may be adifferent type of finger-operated user input device, for example,forming part of a touch screen display. Other or additionalfinger-operated user input devices may be carried by the portablehousing 21.

The electronic device 20 includes a finger biometric sensor 50, whichmay be in the form of one or more integrated circuits (ICs). The fingerbiometric sensor 50 includes an array of electric field sensing pixels31 that are part of an IC carried by the pushbutton switch 24 to sense auser's finger 40 or an object placed adjacent the array of electricfield sensing pixels. Each pixel 37 may be an electric field sensingpixel as disclosed in U.S. Pat. No. 5,940,526 to Setlak et al., forexample, assigned to the present assignee, and the entire contents ofwhich are herein incorporated by reference.

The finger biometric sensor 50 also includes image data output circuitry51 coupled to the array of electric field sensing pixels 31. The arrayof electric field sensing pixels 31 is carried by the pushbutton switch24 so that when a user or object contacts and/or presses downward on thepushbutton switch, the image data output circuitry 51 cooperates withthe array so that image data from the user's finger 40 is acquired, forexample, finger image data for finger matching and/or spoof detection,as will be appreciated by those skilled in the art.

In other words, the array of electric field sensing pixels 31 maycooperate with the image data output circuitry 51 to be responsive tostatic contact or placement of the user's finger 40 or object. Ofcourse, in other embodiments, for example, where the array of electricfield sensing pixels 31 is not carried by a pushbutton switch, the arrayof electric field sensing pixels may cooperate with the image dataoutput circuitry 51 to be responsive to sliding contact (i.e. a slidesensor), or responsive to static placement (i.e. a standalone staticplacement sensor).

Referring now additionally to FIG. 4, a dielectric layer 55 is over thearray of electric field sensing pixels 31. The dielectric layer 55 may aprotective layer of dielectric material or for aesthetics, and, forexample, in some embodiments, may be part of the display 23 and/or mayalso be carried by the pushbutton switch 24. It should be understoodthat the dielectric layer 55 is generally not a passivation layer whenthe finger biometric sensor 50 is in the form of an IC, for example.

The dielectric layer 55 causes an electric field diffusion. The electricfield diffusion causes the image data output circuitry 51 to generateimage data that corresponds to a blurred image. In other words, a fingerimage or fingerprint image generated from image data collected from theuser's finger 40 is blurred, for example, as illustrated in the blurredfinger image 56 in FIG. 5a . A blurred finger image may make itincreasingly difficult to perform, for example, a matching operation,spoof detection operation, or other operation based upon the fingerimage. The electric field diffusion has a diffusion function associatedtherewith, for example, a Gaussian function.

The electronic device 20 also includes deblurring circuitry 34 coupledto the image data output circuitry 51. The deblurring circuitry 34includes a deblurring processor 35 and memory 36 coupled thereto forstoring the image data. The deblurring processor 35 is capable ofprocessing the image data to produce processed image data representativeof a deblurred finger image. For example, a deblurred finger image 57processed by the deblurring circuitry 34 is illustrated in FIG. 5b . Inparticular, the deblurring processor 35 is capable of processing theimage data to produce processed image data in accordance with adeblurring function based upon the diffusion function, for example, aninverse Gaussian function when the electric field diffusion has aGaussian function associated therewith.

It should be understood that in some embodiments, the deblurringcircuitry 34 may be part of or included in the processor 22. In otherwords, the functionality described herein with respect to the deblurringprocessor 35 may be performed by the processor 22, another processor, orshared between or among processors. Similarly, the memory 36 of thedeblurring circuitry 34 may be shared with or included within the devicememory 26.

In some embodiments, the dielectric layer 55 may have a non-uniformthickness. For example, the dielectric layer 55 may be curved, or thenon-uniform thickness may be a result of manufacturing variances (FIG.4) and may have a thickness that varies between 100 um-500 um. Inparticular, for a curved dielectric layer 55, the dielectric layer mayhave a first thickness d1 near the center while the ends may have asecond thickness d2.

The deblurring processor 35 is capable of processing the image data toproduce image data representative of the deblurred finger image basedupon the non-uniform thickness. More particularly, the deblurringprocessor 35 may cooperate with the memory 36 to apply a deblurringfunction that is based also upon the thickness of the dielectric layer55. For example, different coefficients of the deblurring function maybe associated with different thicknesses of the dielectric layer 55 sothat the variations of thickness across the dielectric layer areaccounted for in a deblurring operation. Of course, the deblurringprocessor 35 may perform other or additional deblurring techniques toproduce image data representative of the deblurred finger image basedupon the non-uniform thickness. For example, a given one of multipledeblurring functions may be applied to a region of the array 31 as willbe appreciated by those skilled in the art.

In some embodiments, the deblurring processor 35 is capable of storingdeblurring coefficients for the deblurring function. For example, thedeblurring processor 35 may be capable of storing deblurringcoefficients in the memory 36 based upon a plurality of fingerprintimage simulations. The deblurring coefficients may be generated by thedeblurring processor 35, the processor 22, and/or another processor, forexample, that may be remote from the electronic device 20. Thedeblurring function may be heuristically derived, or a learning functionmay be performed with respect to the coefficients. The deblurringfunction may thus be attempted with different coefficients acrossfingerprint images to determine which coefficients result in increaseddeblurring of the generated image data. Additional techniques may beused for deblurring or reducing the electric field diffusion using ananisotropic dielectric layer, for example as described in U.S. Pat. No.6,088,471 to Setlak et al. and assigned to the present assignee, and theentire contents of which are herein incorporated by reference.

The processor 22 may also cooperate with the array of electric fieldsensing pixels 31 to determine a finger match based upon fingerbiometric data. More particularly, the processor 22 may determine afinger match based upon enrollment data stored in the device memory 26.The processor 22 may also determine a live finger based upon spoof data.More particularly, the processor 22 may determine a live finger basedupon a complex impedance and/or bulk impedance measurement.

In some embodiments, the processor 22 may cooperate with the array ofelectric field sensing pixels 31 to perform a navigation function, forexample. Of course the processor 22 may cooperate with the array ofelectric field sensing pixels 31 and/or other circuitry to perform otheror additional functions, as will be appreciated by those skilled in theart.

The finger biometric sensor 50 also includes drive circuitry 44 coupledto the array of electric field sensing pixels 31 and a finger couplingelectrode 45 adjacent the array of electric field sensing pixels 31 andcoupled to the drive circuitry. The array of electric field sensingpixels 31 cooperates with the drive circuitry 44 to couple the user'sfinger 40 to a reference and generate a detected signal based uponplacement of the user's finger 40 adjacent the array of electric fieldsensing pixels, as will be appreciated by those skilled in the art.Further details of example drive circuitry 44 and finger couplingelectrode are described in U.S. Pat. No. 5,963,679, to Setlak andassigned to the present assignees, and the entire contents of which areherein incorporated by reference. As will be appreciated by thoseskilled in the art, additional noise or finger image compensationtechniques may be used in conjunction with the deblurring circuitry 34.

A method aspect is directed to a finger biometric method that includesoperating a finger biometric sensor 50 that includes an array ofelectric field sensing pixels 31 and image data output circuitry 51coupled thereto. A dielectric layer 55 is over the array of electricfield sensing pixels thereby causing electric field diffusion so thatthe image data output circuitry generates image data corresponding to ablurred finger image. The method includes processing the image datausing deblurring circuitry 34 coupled to the image data output circuitry51 to produce processed image data representative of a deblurred fingerimage.

A non-transitory computer readable medium for finger biometricprocessing aspect includes computer-executable instructions capable ofperforming operations that may include operating a finger biometricsensor 50 that includes an array of electric field sensing pixels 31 andimage data output circuitry 51 coupled thereto. A dielectric layer 55 isover the array of electric field sensing pixels 31 thereby causingelectric field diffusion so that the image data output circuitrygenerates image data corresponding to a blurred finger image. Thecomputer-executable instructions are for also performing the operationprocessing the image data using deblurring circuitry 34 coupled to theimage data output circuitry 51 to produce processed image datarepresentative of a deblurred finger image.

Referring now to FIGS. 6-7, in another embodiment, as will beappreciated by those skilled in the art, it may be desirable to processimage data from sub-arrays 138 of the array of electric field sensingpixels 131, for example, for increased processing speed. When processingimage data from each of the sub-arrays 138, a limited area of theblurred image is generally available, while a larger area of theoriginal fingerprint image from the array 131 was blurred as a result ofthe dielectric layer 155, for example. Because a part of contextualinformation is missing from the limited area of the sub-arrays 138, thepixels 137 near image boundaries (e.g., borders of the array) or betweenadjacent sub-arrays, may not be easily and exactly reconstructed, evenin absence of noise, for example. Additionally, a part of the image datafor deblurring may be lost due to quantization (i.e. sampling andstorage of pixel image data), buried by system noise, or affected byother artifacts (e.g. drive leakage).

To address this image data loss, it may be desirable to exploit priorinformation about the image data, for example, the finger imageproperties and the finger image formation model. Such prior informationmay include typical frequency range of features to recover, model of theblurring process (blurring kernel, frequency characteristics), model ofnoise, etc.

To address image boundaries, for example, at a border of the array, aclassical approach would be to extend the image, and extrapolate themissing pixels using e.g. symmetric boundary conditions. However,deblurring with respect to an array of electric field finger sensingpixels generally differs from a classical deblurring application. Forexample, finger image data, e.g., fingerprint images, are a specificimage category, wherein the frequency range of useful features isdifferent from other image data types.

Additionally, the finger image area for finger biometric sensors may berelatively small compared to other imaging applications. For example, afinger biometric sensor may include an array of 88×88 electric fieldsensing pixel (500 dpi). Compared to the Gaussian blur sigma around 3pixels for a 400 μm total dielectric layer thickness, and counting witha 3-sigma kernel for blurring/deblurring, 9 pixels around each fingerimage border may be considered as “boundary” pixels. In total, thisrepresents more than one third of the electric field sensing pixels. Forsuch a relatively small finger image, boundary conditions may becomeincreasingly important, and classical techniques based on the assumptionof “infinite” spatial extent (such as, for example, Fourier-baseddeconvolution techniques) become unusable.

Additionally, compared to other applications, a finger biometric sensormay have a relatively high level of noise. For example, for 300 μm ridgefeatures, the expected signal-to-noise ratio may be around 0 dB.

The concavity, die warp, or non-parallelism of the array of electricfield sensing pixels 131 versus the dielectric layer 155 over the arraymay lead to different blurring/deblurring kernels for different arraypositions. Drive leakage may also lead to different sensingcharacteristics near the finger image border or image data correspondingto a border of the array, or to exclusion of image regions. Withoutcompensation, this may lead to an irregular finger image boundary.

Additionally, deblurring as it is applied to a finger biometric sensormay be subject to limited computational power. For example, thedeblurring circuitry 134 may be included as part of or implementedwithin a secure processor that may perform other functions of a hostdevice, for example, the electronic device 120. Thus, it may bedesirable that any functions executed by the deblurring circuitry 134 berelatively simple for increased processing speed, for example.

To address the finger image data loss, deblurring circuitry 134 is usedto process the image data from each of the sub-arrays 138. Thedeblurring circuitry 134 may process the image data from adjacent aborder of the array 131 (i.e., a border sub-array) and/or from aninternal sub-array that is spaced inwardly from the border of the array.

The array of electric field sensing pixels 131 has a diffusion functionassociated therewith. The electric field diffusion associated with thearray 131 can be characterized by respective electric field diffusionfunctions for each of the sub-arrays 138.

The deblurring circuitry 134, and more particularly, the deblurringprocessor 135, processes the image data, for example, from each of thesub-arrays 138, which may include both border and internal sub-arrays,in accordance with respective deblurring functions for each of thesub-arrays and based upon the diffusion function. In other words, imagedata from each sub-array 138 is processed according to its respectivediffusion function. This may address blurring at array positions causedby concavity, die warp, or non-parallelism of the array of electricfield sensing pixels 131 versus the dielectric layer 155.

As noted above, the sub-arrays 138 may be along or may overlap a borderof the array of electric field finger sensing pixels 131 (FIG. 7), andpart of the image data or contextual information associated with theimage data may be missing or lost along the border of the array 131. Asub-array 138, for example, for an 88×88 array of electric field sensingpixels, may be an 8×8 sub-array. A sub-array 138 may include a singlepixel in some embodiments. Of course, a sub-array 138 may be anothersize.

Other techniques, for example, Wiener filtering, contrast enhancementfilters, band-pass filtering, etc. have been attempted. In contrast tothese other techniques, increased deblurring results were obtained wheneach diffusion function was estimated based upon a least squares problemor linear regression. To generate each deblurring function, pairs ofreference images and simulated images are formed with blur, noise orother deformations. A deblurring function was attempted that reduces orminimizes the residual error between the original and reconstructedimages, evaluated over a dataset of finger image data. This way, theprior information (e.g., fingerprint properties, blurring model, noisemodel, etc.) may be propagated into the design of each of the deblurringfunctions executed by the deblurring circuitry 134.

To further illustrate the problems associated with a finger imageboundary (i.e., adjacent a border) as described above, image Arepresents a clean, original finger image, and image B represents asimulated finger image with all possible deformations (blur, noise,etc.). Both finger images are of the same size, for example, 88×88pixels. A single pixel of the finger image A or the finger image B maybe written as a(i,j), b(i,j), respectively. A rectangular area,extracted from the image B around pixel (i,j), may be denoted by b(i,j).

Let K(i,j) stand for the deblurring kernel or deblurring circuitryexecuting the deblurring function at position (i,j). The deblurringcircuitry 134 may perform the deblurring functions as a convolutionoperation, for example, wherein a rectangular area of the image B ismultiplied by the coefficients of K and summed to form a single pixel ofthe deblurred image D. To simplify notation, a matrix formulation may beused: the pixels of a rectangular finger image area, or the elements ofthe deblurring kernel or function, are concatenated to form a1-dimensional column vector. Thus, the deblurring for position (i,j) maybe written as:d(i,j)=K(i,j)^(T) ·b(i,j)where d(i,j) is a single output value, K and b are column vectors, and Trepresents the matrix transpose. In the following, the (i,j) coordinatesare omitted with the understanding that a single location of the fingerimages only is still considered.

It may be desirable to find a deblurring kernel K or function so thatthe deblurred image D is as close as possible to the original cleanfinger image A. This can be formulated as a least squares problem, forexample, where the residual error between the deblurred finger image andthe original finger image may be reduced, summed over all finger imagesin the dataset. For a single location, the error norm becomes:

${E( {i,j} )} = {\sum\limits_{z}( {K^{T}{{\cdot b_{z}} - a_{z}}} )^{2}}$where the index z runs over all finger images in the dataset and thedeblurring kernel K is the same for all images.

This is a classical least squares problem, and the optimal kernel K maybe obtained by solving the normal equationK ^(T) ·b·b ^(T) =b·awhere, with a slight modification of notation, the products involvingvectors b and image pixels a have been accumulated over all images fromthe dataset. Note that only a single position (i,j) of the finger imageis still being considered. In this general formulation, each position inthe finger image may lead to different kernel estimation, for example,as will be appreciated by those skilled in the art.

Referring now additionally to the illustrations 158 and 159 in FIGS. 8aand 8b , the kernel K is applied to an area of an image B (correspondingto a sub-array of the array of electric field finger sensing pixels), toobtain a single pixel that is equal to the pixel of the original image A(not shown). This relation is used to formulate the minimization problemand estimate the kernel K or deblurring function from theoriginal-blurred image or sub-array.

For positions adjacent the border of the image or array 131 (FIG. 8b ),a part of the image pixels B are generally valid. Thus, a subset ofdeblurring coefficients for each deblurring function, or the deblurringkernel K, are to be estimated.

The estimation of the deblurring kernel or each deblurring function,including the deblurring coefficients, from the image data will now bedescribed in further detail. The dimension of the deblurring kernel K oreach deblurring function can be chosen, for example, to have a sizebetween 5×5 and 15×15 pixels, centered around each image position. Thekernel size may be indexed by the size from the center, k. A kernel size15×15 corresponds to k=7.

For kernels or deblurring functions inside the finger image (i.e., notadjacent the boundary of the array 131 as illustrated the in FIG. 8a ),a kernel of (2k+1)×(2k+1) pixels has, in general, (2k+1)×(2k+1)deblurring coefficients. The number of deblurring coefficients may bereduced by making assumptions about the image data or kernel symmetry,as will be appreciated by those skilled in the art. Also, a reducednumber of coefficients near the border of the array 131 or finger imageborder may also be used with each deblurring function (FIG. 8b ).

To obtain an increasingly reliable estimate of the large number ofdeblurring coefficients, a relatively good number of training samplesfor the least square problem may be desired. Again, exploitingsymmetries typically reduces the number of finger images or image dataand also may reduce the risk of over-fitting.

In the normal equation above, the products b·b^(T) and b·a areaccumulated from all images in the training set, separately for eachposition:

${X( {i,j} )} = {\sum\limits_{z}{{b_{z}( {i,j} )} \cdot {b_{z}( {i,j} )}^{T}}}$${Y( {i,j} )} = {\sum\limits_{z}{{b_{z}( {i,j} )} \cdot {a_{z}( {i,j} )}}}$For a single position (i,j), note that the dimension of the matrix X is[(2k+1)×(2k+1)]×[(2k+1)×(2k+1)]. For a 15×15 kernel or a deblurringfunction corresponding to a 15×15 sub-array (k=7), X is a 225×225matrix. The column vector Y includes [(2k+1)×(2k+1)] values.

Using X and Y, the normal equations for kernel K can be rewritten into:K ^(T) ·X=YIn some embodiments, the kernel or deblurring function estimation may bean offline process, wherein such estimation or function may besimulated, for example, using a computer program, such as, for example,Matlab®. Of course, other programs may be used to solve such an equationor generate each deblurring function. The kernel for position (i,j) canthen be obtained using matrix division:K ^(T) =Y/X.

Other circuitry or elements illustrated but not specifically describedwith respect to FIGS. 6-7 are similar to those described above withrespect to FIGS. 2-5 and require no further discussion herein. As willbe appreciated by those skilled in the art, while applying the diffusionfunctions to each of the sub-arrays 138 may be particularly advantageousfor deblurring a blurred finger image, the deblurring circuitry 134using the deblurring functions may also be advantageous for reducingfalse positives with respect to finger matching and/or spoof detection.Moreover, by using sub-arrays 138 and applying a linear regression, amore accurate deblurred finger image may result, especially adjacentborders of the array 131.

A method aspect includes operating a finger biometric sensor 150 thatincludes an array of electric field sensing pixels 131 and image dataoutput circuitry 151 coupled thereto. A dielectric layer 155 is over thearray of electric field sensing pixels 131 thereby causing electricfield diffusion so that the image data output circuitry 151 generatesimage data corresponding to a blurred finger image. The method alsoincludes processing the image data using deblurring circuitry 134coupled to the image data output circuitry 151 to produce, from each ofa plurality of sub-arrays 138 of the array of electric field sensingpixels 131 each having a diffusion function associated with the electricfield diffusion, and in accordance with a respective deblurring functionassociated with each diffusion function, processed image datarepresentative of the deblurred finger image.

A non-transitory computer readable medium for finger biometricprocessing includes computer-executable instructions capable ofperforming operations that may include operating a finger biometricsensor 150 that includes an array of electric field sensing pixels 131and image data output circuitry 151 coupled thereto, and with adielectric layer 155 over the array of electric field sensing pixelsthereby causing electric field diffusion so that the image data outputcircuitry generates image data corresponding to a blurred finger image.The operations may also include processing the image data usingdeblurring circuitry 134 coupled to the image data output circuitry 151to produce, from each of a plurality of sub-arrays 138 of the array ofelectric field sensing pixels each having a diffusion functionassociated with the electric field diffusion, and in accordance with arespective deblurring function associated with each diffusion function,processed image data representative of the deblurred finger image.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims.

That which is claimed is:
 1. An electronic device comprising: a fingerbiometric sensor comprising a plurality of sub-arrays of sensing pixels;a dielectric layer over the plurality of sub-arrays of sensing pixelsand causing blurred finger image data; and deblurring circuitry coupledto the finger biometric sensor and configured to store a plurality ofdeblurring coefficients, and process the blurred finger image data usingthe plurality of deblurring coefficients to produce deblurred fingerimage data.
 2. The electronic device of claim 1, wherein the pluralityof deblurring coefficients comprises a respective set of deblurringcoefficients for each of a plurality of different deblurring functions.3. The electronic device of claim 2, wherein the deblurring circuitry isconfigured to process the blurred finger image data based upon arespective deblurring function for each sub-array of electric fieldsensing pixels.
 4. The electronic device of claim 1, wherein theplurality of sub-arrays of sensing pixels define an array having aborder; and wherein the plurality of sub-arrays of sensing pixelscomprises at least one border sub-array of sensing pixels adjacent tothe border.
 5. The electronic device of claim 1, wherein the pluralityof sub-arrays of sensing pixels define an array having a border; andwherein the plurality of sub-arrays of sensing pixels comprises at leastone internal sub-array of sensing pixels spaced inwardly from theborder.
 6. The electronic device of claim 1, wherein the blurred fingerimage data is based upon a diffusion function; and wherein thedeblurring circuitry is configured to process the blurred finger imagedata in accordance with respective different deblurring functions foreach of the plurality of sub-arrays of sensing pixels based upon thediffusion function.
 7. The electronic device of claim 6, wherein thediffusion function comprises a Gaussian function and the respectivedeblurring functions each comprises an inverse Gaussian function.
 8. Theelectronic device of claim 1, wherein the dielectric layer has anon-uniform thickness.
 9. The electronic device of claim 1, wherein thedeblurring circuitry comprises a deblurring processor and memory coupledthereto.
 10. The electronic device of claim 1, wherein the fingerbiometric sensor further comprises drive circuitry coupled to theplurality of sub-arrays of sensing pixels.
 11. The electronic device ofclaim 10, wherein the finger biometric sensor comprises a fingercoupling electrode adjacent the plurality of sub-arrays of sensingpixels and coupled to the drive circuitry.
 12. A method for fingerbiometric sensing comprising: operating a finger biometric sensorcomprising a plurality of sub-arrays of sensing pixels and a dielectriclayer thereover causing blurred finger image data; and processing theblurred finger image data using a plurality of stored deblurringcoefficients to produce deblurred finger image data.
 13. The method ofclaim 12, wherein the plurality of deblurring coefficients comprises arespective set of deblurring coefficients for each of a plurality ofdifferent deblurring functions.
 14. The method of claim 13, whereinprocessing comprises processing the blurred finger image data based upona respective deblurring function for each sub-array of sensing pixels.15. The method of claim 12, wherein the plurality of sub-arrays ofsensing pixels define an array having a border; and wherein theplurality of sub-arrays of sensing pixels comprises at least one bordersub-array of sensing pixels adjacent to the border.
 16. The method ofclaim 12, wherein the plurality of sub-arrays of sensing pixels definean array having a border; and wherein the plurality of sub-arrays ofsensing pixels comprises at least one internal sub-array of sensingpixels spaced inwardly from the border.
 17. The method of claim 12,wherein the blurred finger image data is based upon a diffusionfunction; and wherein processing comprises processing the blurred fingerimage data in accordance with respective different deblurring functionsfor each of the plurality of sub-arrays of sensing pixels based upon thediffusion function.
 18. The method of claim 17, wherein the diffusionfunction comprises a Gaussian function and the respective deblurringfunctions each comprises an inverse Gaussian function.
 19. Anon-transitory computer readable medium for finger biometric processing,the non-transitory computer readable medium comprisingcomputer-executable instructions configured to perform operationscomprising: operating a finger biometric sensor comprising a pluralityof sub-arrays of sensing pixels and a dielectric layer thereover causingblurred finger image data; and processing the blurred finger image datausing a plurality of stored deblurring coefficients to produce deblurredfinger image data.
 20. The non-transitory computer readable medium ofclaim 19, wherein the plurality of deblurring coefficients comprises arespective set of deblurring coefficients for each of a plurality ofdifferent deblurring functions.
 21. The non-transitory computer readablemedium of claim 20, wherein processing comprises processing the blurredfinger image data based upon a respective deblurring function for eachsub-array of sensing pixels.
 22. The non-transitory computer readablemedium of claim 19, wherein the plurality of sub-arrays of sensingpixels define an array having a border; and wherein the plurality ofsub-arrays of sensing pixels comprises at least one border sub-array ofsensing pixels adjacent to the border.
 23. The non-transitory computerreadable medium of claim 19, wherein the plurality of sub-arrays ofsensing pixels define an array having a border; and wherein theplurality of sub-arrays of sensing pixels comprises at least oneinternal sub-array of sensing pixels spaced inwardly from the border.24. The non-transitory computer readable medium of claim 19, wherein theblurred finger image data is based upon a diffusion function; andwherein processing comprises processing the blurred finger image data inaccordance with respective different deblurring functions for each ofthe plurality of sub-arrays of sensing pixels based upon the diffusionfunction.
 25. The non-transitory computer readable medium of claim 24,wherein the diffusion function comprises a Gaussian function and therespective deblurring functions each comprises an inverse Gaussianfunction.